Ultrasonic flow meter including a meter housing insert having transducer recesses with slanted bottom walls

ABSTRACT

An ultrasonic flow meter including a meter housing, a flow tube with an inner flow channel for a fluid to be measured, and ultrasound reflectors, the meter housing has two transducer recesses, an ultrasound transducer positioned in the first transducer recess, and a second ultrasound transducer positioned in the second transducer recess. The transducer recesses each has slanted bottom walls, with the ultrasound transducers abutted against the slanted bottom walls of the recesses.

FIELD OF THE INVENTION

The invention relates to an ultrasonic flow meter for measuring the flowof a fluid.

BACKGROUND OF THE INVENTION

Several ultrasonic flow meters exists within the prior art.

An example of such flow meters is found in the European patentapplication 0 440 867 A1, where the transducers are inserted in bevels.

Another example of an ultrasonic flow meter is found in U.S. Pat. No.5,351,560, having a W-shaped ultrasonic path and where an inner wall hasa stepped elevation/depression at the reflection site of the V-shapedparasitic ultrasonic path.

Yet another example of an ultrasonic flow meter is found in U.S. Pat.No. 5,372,047, having reflection points, which have a focusing effect onan ultrasonic beam.

A problem related to the above mentioned prior art is how to provide anefficient and cost-effective ultrasonic flow meter and the assembly ofsuch flow meters.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a compact ultrasonic flowmeter.

It is a further object of the invention to provide an efficient andcost-effective ultrasonic flow meter and a method for assembling such anultrasonic flow meter.

The invention relates to an ultrasonic flow meter comprising

-   -   a meter housing,    -   a flow tube defining an inner flow channel for a fluid to be        measured, and    -   one or more ultrasound reflectors,        said meter housing comprising    -   a first transducer recess,    -   a second transducer recess,    -   a first ultrasound transducer positioned in said first        transducer recess,    -   a second ultrasound transducer positioned in said second        transducer recess, and    -   an electronic circuit for operating said ultrasonic flow meter,        wherein said transducer recesses each has slanted bottom walls,        and

wherein said first and second ultrasound transducers are in abutmentwith said slanted bottom walls of said first and second transducerrecess, respectively.

In the present context it is to be understood that said first ultrasoundtransducer is in abutment with said slanted bottom wall of said firsttransducer recess and that said second ultrasound transducer is inabutment with said slanted bottom wall of said second transducer recess.

The ultrasonic flow meter is adapted to measure the average flowvelocity of the fluid. This may preferably be done by said firstultrasound transducer emitting a first ultrasound pulse. The firsttransducer is positioned such that the first ultrasound pulse isincident on the first ultrasound reflector, which reflects the firstultrasound pulse towards the second ultrasound transducer, which thenreceives or detects the first ultrasound pulse. Thereby, a first pathfrom the first ultrasound transducer, via the first ultrasoundreflector, and onto the second ultrasound transducer is defined.Similarly, the second ultrasound pulse is sent from the secondultrasound transducer, via the first ultrasound reflector and onto thefirst ultrasound transducer, thereby defining a second path. Bymeasuring a first transit time as the time between emitting anddetecting the first ultrasound pulse, and a second transit time as thetime between emitting and detecting the second ultrasound pulse, themean velocity of the fluid can be calculated from the two transit timesand the geometry of the transducers and reflectors.

Said first ultrasound reflector is adapted to reflect the ultrasound,thereby redirecting the path of the ultrasound beam from one ultrasoundtransducer to the other ultrasound transducer.

When said transducer recesses extend into the flow tube, a particularadvantage of the invention is achieved. This is that due the ultrasoundtransducers being slanted relative to the transducer recesses, theseultrasound recesses can be constructed with a smaller diameter orcross-sectional area, whereby the tube openings can be made with asmaller diameter or area. Since these areas are reduced, the pressureexerted by the fluid in the flow channel upon the transducer recessesextending into the flow channel can be reduced. This results in reducedthe minimum limits on material strength and on the construction design,which are a result of this fluid pressure. A result from these reduceslimitations is that a more compact flow meter may be constructed, due toe.g. reduced need for connection strength between the meter housing andthe flow tube.

Another advantage of the invention may be that the meter housingincluding its components may be assembled as a single mechanical unit.Thereby, the ultrasonic flow meter may be produced and assembled in asimple and cost-effective way.

Yet another advantage of the invention may be that since the ultrasoundtransducers have a slanted orientation, flow tubes of differentdiameters may be fitted to the same meter housing. Only the positionand/or the orientation of the one or more ultrasound reflectors have tobe changed. Preferably, the ultrasound reflectors may be fixated by aflow channel insert. Thereby, for each flow tube with differentdiameters, a flow channel insert may be constructed that fits theparticular tube, and which furthermore includes ultrasound reflectors inthe adjusted positions and orientations so that an ultrasound signalreflected by the first ultrasound transducer propagates via theultrasound reflectors to the second ultrasound transducer. Since themeter housing may typically represent the main expenses of the tools forproduction of the ultrasonic flow meter it may be expensive to producedifferent meter housings for each flow tube diameter. However, since ameter housing can be fitted to flow tubes of different diameters, thisextra cost may be avoided or reduced.

One particular advantage of the invention may be that the housing andthe first and second meters are all in physical connection with eachother thereby forming a single unit. Thereby it may be substantiallyeasier to comply with various tolerances that such meters typically mustcomply with. In more detail, by putting said first and secondtransducers in abutment with said slanted bottom walls of saidtransducer recesses, preferably by making physical contact between eachof the transducers and the corresponding bottom wall of thecorresponding transducer recess by means of e.g. conductive adhesive,electrical connectivity between the transducer and the contactpositioned on the bottom wall is obtained and, furthermore, a relativelyrigid fixation of the transducer relative to the housing, and, thereby,relative to the other transducer is obtained.

One further advantage of the invention is that by using slantedtransducer recesses an ultrasound path between said first to said secondtransducer, or vice versa, can be constructed such that the ultrasoundpath at all points have a component in a longitudinal direction of theflow tube, i.e. the path is non-orthogonal to the longitudinal directionof the flow tube at all points. Thereby, the whole of the ultrasoundpath are affected by the flow of the fluid to be measured, and,therefore, contributes to a more precise and accurate measurement. Inother words, a flow meter of the present invention may achieve arelatively high signal-to-noise rate compared to other solutions,without said meter of the invention employing power-depleting measures,such as transmitting a stronger signal and/or repeating the measurementseveral extra times and performing an average. This may be a particularadvantage for battery-powered meters, and may even be for externallypowered meters, should such meters loose the external powering and haveto rely on a backup battery power source.

One particularly advantageous aspect of the invention may be that thefirst and second transducers are both placed inside and as a part of themeter housing. Thereby, it is to be understood that an ultrasound signalemitted by the first ultrasound transducer, and reflected by the one ormore ultrasound reflectors, before being detected by the secondtransducer, will propagate from the emitting surface of the firsttransducer through the slanted bottom wall of the e first transducerrecess, through the fluid in the flow channel, reflected by the one ormore ultrasound reflectors while still propagating through the fluid,and through the slanted bottom wall of the second transducer recess,before finally reaching the transmitting surface of the secondultrasound transducer where the ultrasound signal is detected andtransformed into an electrical signal by the second transducer.

One further advantage of the invention may be that aggregation of gasbubbles on the transducer-fluid interface may be avoided even if theflow tube is orientated with the meter display upwards, which may oftenbe preferred by consumers, since this orientation permits easy readoutof the display. However, when the display is faced upwards, thetransducers in typical compact meter setups will be located in the upperpart of the flow tube. Since gas bubbles, such as air bubbles, may oftenbe released by the fluid, e.g. air bubbles from water, these gas bubblesmay often aggregate near the highest point in the flow tube due togravity. Such aggregation of gas bubbles near on the meter-fluidinterface is highly disadvantageous, since the efficiency of thecoupling of ultrasound between the transducers and the fluid becomesrelatively low. However, since the transducer recesses are slanted, suchgas bubbles may not aggregate on meter-fluid interface, but rather moveupwards along the slanted bottom walls of transducer recesses and awayfrom at least position on the meter-fluid interface corresponding to thecenter of the transducer.

According to an embodiment of the invention, it is to be understood thata transducer recess is a local extension of the inner space of the meterhousing, in which an ultrasound transducer may be positioned. Thereby,the ultrasound transducer can emit an ultrasound signal through theslanted bottom wall of the transducer recess and into the flow channelof the ultrasonic flow meter, and vice versa receive an ultrasoundsignal through propagating through said slanted bottom wall of saidtransducer recess.

According to an embodiment of the invention, the ultrasonic flow meteris adapted for measuring a flow velocity of a fluid flowing through theflow channel. This fluid may be liquids as well as gasses, particularlyliquids such as water.

According to an embodiment of the invention, said first and a secondtransducer recess extends through a first and a second tube opening insaid flow tube and into said flow channel.

Thereby, in the context of the above embodiment it is particularlyadvantageous that the size of the transducer recesses is reduced,thereby reducing the pressure from the fluid on the meter housing.

According to an embodiment of the invention, said ultrasound transducersare positioned inside said meter housing, and wherein at least one ofsaid ultrasound transducers is configured for, during operation of saidultrasonic flow meter, to emit an ultrasound signal, said ultrasoundsignal propagating through said slanted bottom wall abutting said atleast one ultrasound transducer, through said fluid in said flowchannel, and said ultrasound signal being reflected by said one or moreultrasound reflectors, then propagating through said slanted bottom wallabutting the other ultrasound transducer receiving said ultrasoundsignal.

According to an embodiment of the invention, said first ultrasoundtransducer and said one or more ultrasound reflectors are positioned andorientated so that if, during operation of said ultrasound flow meter, afirst ultrasound signal is emitted from said first transducer, saidfirst ultrasound signal is reflected by said one or more ultrasoundreflectors and detected by said second ultrasound transducer, and viceversa if said second ultrasound transducer emits a second ultrasoundsignal it is detected by said first ultrasound transducer.

According to an embodiment of the invention, said first and secondultrasound transducers are positioned and orientated so that when,during operation of said ultrasonic flow meter, a first ultrasoundsignal is transmitted from said first ultrasound transducer, said firstultrasound signal will propagate through said slanted bottom wall ofsaid first transducer recess, through the fluid in the flow channel,reflected by said one or more reflectors, and through said slantedbottom wall of said second transducer recess, before being detected bysaid second ultrasound transducer, and vice versa a second ultrasoundsignal may be transmitted from said second ultrasound transducer to saidfirst ultrasound transducer through said slanted bottom walls of saidtransducer recesses.

By a slanted bottom wall may in one embodiment be meant a bottom wall,where the surface this bottom wall is non-orthogonal to the directionthe side walls of the transducer recess, i.e. an inclined bottom wall.Here it should be noted that the longitudinal axis of the recess isdefined by the sides of the recess. Thereby, the longitudinal axes ofthe transducer recesses are preferably orientated orthogonal with alongitudinal axis of the flow tube. A particular aspect of the inventionis that the first and second transducers are both placed in the meterhousing. Thereby, it is to be understood that an ultrasound signalemitted by the first ultrasound transducer, and reflected by the one ormore ultrasound reflectors, before being detected by the secondtransducer, will propagate from the emitting surface of the firsttransducer through the slanted bottom wall of the e first transducerrecess, through the fluid in the flow channel, reflected by the one ormore ultrasound reflectors while still propagating through the fluid,and through the slanted bottom wall of the second transducer recess,before finally reaching the transmitting surface of the secondultrasound transducer where the ultrasound single is detected andtransformed into an electrical signal by the second transducer. Anexample of such a transducer recess with a slanted bottom wall is a tubeextending from the meter housing, and having a bottom wall the surfaceof which is being non-orthogonal to a longitudinal axis of the tube.

I.e. said housing comprises a first transducer recess, in which thefirst ultrasound transducer is positioned, and a second transducerrecess, in which the second ultrasound transducer is positioned.

It is to be noted that since the transducer recesses each have a slantedbottom wall on which the ultrasound transducer is positioned, said firsttransducer has a first ultrasound transmitting surface and said secondtransducer has a second ultrasound transmitting surface, wherein saidfirst and second transmitting surfaces have a non-orthogonal orientationwith respect to a longitudinal axis of said first and second transducerrecess, respectively. Also, one can equivalently define the orientationof the ultrasound transducers by said first and second ultrasoundtransmitting surfaces being non-parallel to a longitudinal axis of theflow channel. Yet another way of defining the orientation of the firstand second ultrasound transducers is that the path of an ultrasoundsignal emitted by the first or second ultrasound transducer will benon-parallel to the longitudinal axes of the first and second transducerrecesses, and also non-orthogonal to the longitudinal axis of the flowtube.

According to an embodiment of the invention, said longitudinal axis ofeach elongated transducer recesses is orthogonal with respect to alongitudinal axis of the flow channel.

Thereby, the assembly of the ultrasonic flow meter is made easy, since asingle-piece meter housing can be inserted through tube openings in theflow tube and into the flow channel. Since this insertion is done bymoving the meter housing in a direction orthogonal to longitudinal axisof the flow channel, this insertion is simple, and furthermore, the tubeopenings can be constructed with a size and form fitting thecross-sectional size and form of the transducer recesses, e.g. byfitting the diameter of the tube openings to the diameter of transducerrecess for cylindrical transducer recesses.

According to an embodiment of the invention, the ultrasonic flow metercomprises a first, a second, and a third ultrasound reflector).

It is preferred that the ultrasonic flow meter comprises threeultrasound reflectors, preferably positioned in a so-called W-geometry.By a W-geometry is meant a position and orientation of the ultrasoundtransducers and the ultrasound reflectors such that the path of theultrasound signal takes the form of a W when viewed from the side.Thereby, the path length of the ultrasound may be maximized to give alonger transit times. By increasing the transit times, it may be securedthat the signal-to-noise ratio may be decreased, even for a compact flowmeter. This is especially true for ultrasonic flow meters that inaddition to a transit time differences includes an absolute transit timefor flow measurements.

However, in alternative embodiments, only a single or two ultrasoundreflectors are used. In some embodiments, where flow tubes of largerdiameter are used it may be particularly advantageous to use only asingle ultrasound reflector.

According to an embodiment of the invention, said housing comprises abattery.

Thereby, the ultrasonic flow meter may be independent of an externalpower supply. One particular advantage of the above embodiment may bethat a meter may be more energy efficient, while retaining the samesignal-to-noise ratio.

When each of said transducer recesses has a slanted bottom wall, andwhen said first and second ultrasound transducers each are in abutmentwith the corresponding slanted bottom wall of the correspondingtransducer recess, the path of the ultrasound from said first to saidsecond transducer, or vice versa, may be constructed such that the pathhave at least a non-zero component parallel with the longitudinal axisof the flow channel, i.e. the overall flow direction. As only thecomponents of an ultrasonic path, which are parallel to the flowdirection, contributes to a time delay, and therefore to the measurementof the flow, the meter according to the above embodiment may beconstructed to give a higher signal without the use of additionalreflectors. As many ultrasound meters may use transducers emitting asignal travelling substantially orthogonal to the flow direction, thepath of the ultrasound in such meters between the emitting transducersand the first reflecting ultrasound reflector along the ultrasound pathdoes not contribute to the measurement of the flow, but only contributenoise and/or attenuation of the signal, therefore lowering thesignal-to-noise ratio. Typically, this may be compensated bytransmitting a stronger signal or taking an average over severalmeasurements. The inventor of the present invention, however, hasrealized that such power-depleting measures may be avoided, or at leastminimized, by using transducers emitting ultrasound in a non-orthogonaldirection relative to the flow direction.

According to an embodiment of the invention, said one or more ultrasoundreflectors consists of three ultrasound reflectors.

Thereby, an ultrasonic signal emitted by said first ultrasoundtransducer and detected by said second ultrasound transducer, or viceversa, is reflected exactly three times by three different ultrasoundreflectors.

In the present context of the above embodiment it should be understoodthat the ultrasonic flow meter comprises exactly three ultrasoundreflectors used to reflect ultrasound between said first and secondtransducer. Thereby, a relatively high signal-to-noise ratio may beachieved and a rather precise measurement may be performed withoutemploying alternative power-depleting measures, such as e.g. increasingthe strength of the emitted signal or repeating the measurement severaltimes.

According to an embodiment of the invention, said housing comprises adisplay.

By said meter housing including a battery and a display, a simplisticdesign may be achieved where no need for external wiring is needed forpower supply or communication. This may be a great advantage in theproduction of the meter, for the user who does not have to connect powersupply or read-out equipment, and furthermore since the housing may besealed to as to extend the life-time of the meter.

Furthermore, by incorporating all electronic equipment in the meterhousing, the need for any external wiring to the meter is eliminated.

According to an embodiment, the paths of the ultrasound will lie withina longitudinal symmetry plane of the flow chamber, i.e. the parts of thepath will span only a single plane parting the flow chamber in twoequal-sized parts along the longitudinal direction. Alternatively,however, the ultrasound reflectors and possibly the transducers may beorientated such that the parts of the ultrasound paths do not fallwithin a single plane.

According to an embodiment of the invention, said ultrasound transducershave a bottom side facing the bottom walls of the first and secondtransducer recesses, and wherein the meter housing comprise a metallayer contact being in electrical contact with the bottom sides of theultrasound transducers and in electrical contact with the electroniccircuit.

By means of the metal layer, electronic contact is facilitated betweenthe bottom sides of the ultrasound transducers and the electroniccircuit. Such contact may otherwise be difficult to establish and mayrequire a tedious assembly process. Furthermore, the metal layerprovides compact electrical connections and thereby allows the assemblyof a compact ultrasonic flow meter.

One particular advantage of the above embodiment may be thatsubstantially the whole of the surface of the transducer may beeffective as an ultrasound emitting surface. Otherwise, e.g. if thetransducer has a wrap-around contact, i.e. where the contact facing theflow tube extends onto the opposite side of the transducer for easieraccess for electrical connections, the effective area of the transducer,which emits ultrasound, may be substantially diminished. Therefore, whenusing such a metal layer contact, the overall area of the transducer canbe lowered, and therefore the area of the transducer recesses may belowered. This, furthermore, may be a substantial advantage, as thestructural strength of the meter housing, the locking pins, etc. may bedetermined by such parameters as the pressure of the fluid in the flowchannel and the area of the holes in the flow tube through which thetransducer recesses extends, or extends at least partly. Thereby,dimensioning of the meter housing, pins, etc. may not be as critical,which may lower the material costs, assembly costs etc.

It is to be understood that this bottom side is the transmitting side ofthe ultrasound transducers, which during operation of the ultrasonicflow meter can emit or detect an ultrasound signal.

Another advantage of the above embodiment is that it is possible to usesmaller transducers, such as smaller piezoelectric elements of thetransducers. By using smaller transducers, the protrusions of the meterhousing, which extends into the flow channel, may be decreased,resulting in a decreased pressure on the meter housing from the fluid inthe flow channel. Such as pressure may indeed be very high, and may callfor a forceful connection between the meter housing and the flow channeltube. However, by decreasing this pressure, such measures may not needto be taken into account, at least to a lesser degree.

According to an embodiment of the invention, each of the ultrasoundtransducers have an upper side connected to a first and a second elasticcontact, respectively.

By an elastic contact is meant a flexible or spring-like contact.However, a coil spring may be unsuitable for contacting with thetransducers, since these are orientated with an angle relative to thelongitudinal axis of the flow chamber and therefore also relative to themeter housing. It may therefore be preferred to use a metal strip, whichmay be curved, to provide a flexible contact suitable for connectingsaid transducers to the electronic circuit.

Furthermore, since such elastic contacts may provide a force towards theflow chamber, or at least a force with a substantial component in adirection towards the flow chamber, the transducer may be fixated bythis force. This may provide with improved electrical contact not onlybetween the elastic contact and the transducer, but also between thetransducer and the metal layer, or at least an ensured contact, i.e.less probability of loss of electrical connection.

In connection with the above embodiment, it should be understood thatsaid upper and lower sides are to be understood as two opposing sides ofthe transducer. Since the transducers have an emitting surface, which isorientated with an angle relative to the longitudinal axis of the flowchamber, the lower side is to be understood as the emitting surface ofthe transducer, which faces the flow chamber, while the upper sideshould be understood as the opposite side or surface relative to thelower side.

Another advantage of the above embodiment is that it is possible to usesmaller transducers, such as smaller piezoelectric elements of thetransducers. By using smaller transducers, the protrusions of the meterhousing, which extends into the flow channel, may be decreased,resulting in a decreased pressure on the meter housing from the fluid inthe flow channel. Such as pressure may indeed be very high, and may callfor a forceful connection between the meter housing and the flow channeltube. However, by decreasing this pressure, such measures may not needto be taken into account, at least to a lesser degree.

Furthermore, since metal spring contacts may traditionally be used toprovide electrical connection between the electronic circuit and thetransducers, and since such metal springs are unsuitable for use withslanted transducers due to a geometric misfit, such slanted transducersmay traditionally be considered disadvantageous. However, the elasticcontacts provide a simple solution for using the slanted transducers.

According to an embodiment of the invention, the elastic contactscomprise curved metal strips.

According to an example embodiment the transducers are piezoelectricelements. By contacting two opposing sides of such a piezoelectricelement to an electrical power source, and by means of the electricalpower source putting an alternating voltage across the piezoelectricelement, the piezoelectric element vibrates according to the alternatingvoltages thereby generating an acoustic signal, such as an ultrasoundsignal.

According to an embodiment of the invention, the ultrasound transducersare focused.

By focusing the ultrasound signal by using focused transducers, severaladvantages are obtained. One of these advantages is that the intendedsignal, i.e. the signal following the first or second ultrasound path,may be transmitted more efficiently from the first transducer to thesecond transducer and vice versa. Another advantage is that unintendedultrasound paths, such as the V-path, will be transmitted lessefficiently between the two ultrasound transducers.

According to an embodiment of the invention, the ultrasonic flow meterfurthermore comprises a flow channel insert.

Such a flow channel insert may provide a single and thereforecost-effective assembly of the compact flow meter. Furthermore, such aflow channel insert may provide fixation of ultrasonic reflectors,narrowing of the room in which the fluid may flow resulting in a higherflow velocity, guiding of the fluid to increase the overlap with theultrasound path, blocking or otherwise discrimination of un-wanted orparasitic ultrasound paths.

Preferably, such a flow channel insert may be assembled from twohalf-parts, preferably mirror-symmetrical.

According to an embodiment of the invention, said one or more ultrasoundreflectors are fixated in said flow channel insert.

For example, the ultrasound reflectors may be fixated in the flowchannel insert in the assembly of the flow channel insert, preferably byassembling the flow channel insert from two half-parts and fitting theultrasound reflectors in between the half-parts. By said ultrasoundreflectors being fixated to said flow channel insert, it is to beunderstood that the ultrasound reflectors may form a part of the flowchannel insert.

According to an embodiment of the invention, said flow channel insert isassembled from two mirror-symmetrical half-parts, the assembled flowchannel insert having a partition surface between the half-parts, saidpartition surface extending from the side of said flow tube facing themeter housing to the opposite side of said flow tube.

According to an alternative embodiment, the partition surface extendsacross the flow tube in substantially the same distance from said meterhousing. I.e. one side of the partition surface faces the meter housing,while the opposite side faces away from said meter housing.

However, the above embodiment where the partition surface extends fromthe side of said flow tube facing the meter housing to the opposite sideof said flow tube may be preferred, since all ultrasound reflectors maybe positioned in the partition surface in that embodiment. This may be aparticular advantage during assembly of the ultrasonic flow meter, sincenone of the ultrasound reflectors need to be embedded into any of thehalf-parts. Rather each ultrasound reflector may simply be fixated bysymmetrical recesses in each of the two half-parts.

According to an embodiment of the invention, the flow channel insertcomprises guide elements for guiding the flow of the fluid.

By said guide elements the flow of the fluid through the flow channelinsert is modified to provide a greater spatial overlap between the flowpath and the ultrasound signal path. This effect is especiallypronounced for smaller meters. By increasing the overlap, theinteraction may also be increased, which leads to a greater differencein upwards and downwards travel times, which in turn may result in alesser uncertainty in the measurement of the velocity of the fluid flowby decreasing the signal-to-noise ratio.

Furthermore, since the guide elements may protrude into the inner spaceof the flow chamber, they may along with the rest of the flow channelinsert contribute to an increased local pressure of the fluid in theflow channel insert, which leads to a greater difference between theupwards and the downwards transit times of the ultrasound signal,thereby decreasing the relative uncertainty of the measured fluid flowvelocity.

According to an embodiment of the invention, the guiding elements of theflow channel insert are adapted for extinguish ultrasound.

By extinguish is meant that the guiding element discriminates againstany ultrasound signal which is incident in the surface of the guidingelement. The physical mechanisms of this extinguishing may be different,such as e.g. blocking or absorbing the ultrasound signal, by scatteringthe ultrasound signal, or by redirecting ultrasound signal such that itto a lesser degree reaches the which should detect the ultrasound signalwith the correct travel path. Such redirection may e.g. be by defocusingor reflection in a certain direction etc. Defocussing may e.g. be doneby a convex surface. This effect gives the advantage of interfering andpossibly blocking alternative paths of the ultrasound pulses from thefirst transducer to the second transducer and vice versa, such as e.g.the so-called V-path.

According to an embodiment of the invention, one or more of theultrasound reflectors are focusing.

This may preferably be done by using concave reflectors. Alternatively,it may be done by means of lens-like objects in front of the reflectors,or a combination thereof concave mirror and lens-like objects. Thisdiscriminates between the W-path and other paths, which are un-wanted orparasitic, such as the V-path, by increasing the signal from the W-path.

According to an embodiment of the invention, reflective surfaces of thefirst and third ultrasound reflectors are orientated such that thesereflective surfaces have angle with respect to the longitudinal axis ofthe flow channel.

In the present context having an angle with respect to the longitudinalaxis of the flow channel is to be understood as the reflecting surfaceof the ultrasound reflector being non-parallel to the longitudinal axis.In cases where the ultrasound reflectors are non-plane, it is to beunderstood that the ultrasound reflector according to the presentembodiment is orientated such that the plane surface, which makes thebest approximation for the reflective non-plane surface, is non-parallelwith the longitudinal axis. Such a best approximation could e.g. be theplane, which gives the same direction of propagation of the reflectedultrasound signal as the actual reflector does.

An advantage of the above embodiment is that the same meter housing maybe fitted to different flow channel tubes of different diameters withoutchanging the orientation of the ultrasound transducers. Instead, thenon-parallel ultrasound reflectors may be positioned and orientatedaccording to the geometry of the flow channel tube, e.g. by fixation ofthe ultrasound reflectors in different flow channel inserts adapted tofit the respective flow channel tubes. Thereby, only a single type ofmeter housings has to be produced, and since tools to produce this partmay constitute a dominant part of the manufacturing expenses, this is agreat advantage. Also, existing meter housings may be adapted to otherflow channel tubes without adjustment of the ultrasound transducers.

A further advantage of using slanted reflectors is that this may preventthe collection of debris from the fluid in the reflectors, or at leastdecrease the effect of such debris collection. Though some debris maycollect on the reflector, due to the asymmetry orientation of thereflector, the debris collection may be largely confined to areas nearthe edge of the reflector, which thereby maintains a high reflectivelyof the ultrasound signal.

According to an embodiment, the one or more ultrasound reflectors arefixated to the flow channel insert. This may e.g. be done by assemblingthe flow channel insert from two symmetrical elements, which whenassembled lock together about the one or more ultrasound reflectors.

According to an embodiment of the invention, the flow channel insert isfixated relative to the flow tube by the meter housing.

This fixation may e.g. be provided by letting the meter housing have twoprotrusions containing the two ultrasound transducers. These twoprotrusions may then extend into the flow channel.

According to an embodiment of the invention, the meter housing isfixated relative to the flow tube by one or more locking pins.

By means of one or more of the above embodiments, the flow meter may beassembled by said flow channel insert fixating said ultrasoundreflectors, furthermore by said meter housing fixating said flow channelinsert, and finally by said meter housing being fixated to said flowchannel by means of a split insert. Thereby, an advantageous assemblymethod for assembling said flow meter is provided. One advantage of thisassembly method is that it may be done without adjusting the orientationof transducers and/or ultrasound reflectors, as these are determinedfrom their respective holding means, i.e. the meter housing for thetransducers and the flow channel insert for the ultrasound reflectors.

The invention furthermore relates to a method of assembling anultrasonic flow meter, said ultrasonic flow meter comprising

-   -   a meter housing,    -   a flow tube defining an inner flow channel for a fluid to be        measured, and    -   a flow channel insert,        said flow channel insert comprising    -   one or more ultrasound reflectors and    -   a first and a second insert opening,        said meter housing comprising    -   a first transducer recess,    -   a second transducer recess,    -   a first ultrasound transducer positioned in said first        transducer recess,    -   a second ultrasound transducer positioned in said second        transducer recess, and    -   an electronic circuit for operating said ultrasonic flow meter,        wherein said transducer recesses each has slanted bottom walls,        and

wherein said first and second ultrasound transducers are in abutmentwith said slanted bottom walls of said first and second transducerrecess, respectively,

said method comprising the steps of

-   -   inserting said flow channel insert into said flow channel,    -   inserting said first and second transducer recesses through said        first and second tube openings and into said first and second        insert openings, and    -   fixating said meter housing to said flow tube.

Thereby, a simple method of assembling an ultrasonic flow meter isprovided, which is efficient and cost-effective. This is an advantage ofthe invention.

According to an embodiment of the invention, the method according to theabove embodiment is provided for of assembling an ultrasonic flow meteraccording to any embodiment of the invention.

FIGURES

The invention will be described in the following with reference to thefigures in which

FIG. 1 illustrates a cross-sectional view of an ultrasonic flow meteraccording to an embodiment of the invention,

FIG. 2 illustrates a cross-sectional view of an ultrasonic flow meterprior to assembly of the meter housing with the flow tube according toan embodiment of the invention,

FIG. 3 illustrates the parts of a cross-sectional view of an ultrasonicflow meter according to an embodiment of the invention,

FIG. 4 illustrates the flow path and the path of an ultrasound signalaccording to an embodiment of the invention,

FIGS. 5A and 5B illustrates an ultrasonic flow meter and a method ofassembling this according to an embodiment,

FIG. 6 illustrates a cross-sectional view of an ultrasonic flow meterwith focusing transducers according to an embodiment, and

FIGS. 7A, 7B, and 7C show schematic illustrations ultrasonic flow meterswith different flow tube diameters of according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an embodiment of the invention is illustrated. Anultrasound flow meter 1 is shown; the ultrasound flow meter 1 comprisinga meter housing 2, a flow tube 20, and a flow channel insert 12. Themeter housing 2 comprises an electronic circuit 4, a battery, a firstand a second transducer recess 15, 16, a first and a second transducer6, 7, a first and a second elastic contacts 24, 25, a metal layercontact 26, and a display 23. The electronic circuit 4, which is poweredby the battery 3, and which is in contact with the first and a secondtransducer 6, 7 via the first and the second elastic contact 24, 25 andthe metal layer contact 26, which comprises a metal layer and an elasticpart. The first and second ultrasound transducers 6, 7 are positioned inthe first and second transducer recesses 15, 16, respectively. As can beseen on FIG. 1, these transducer recesses 15, 16 each have slantedbottom walls 17. Since the first and second transducers 6, 7 arepositioned in the bottom of the transducer recesses 15, 16, ultrasoundemitting surfaces 36 of the ultrasound transducers 6, 7 are for eachtransducer 6, 7 orientated non-orthogonal with respect to a longitudinalaxes 18 of the transducer recesses 15, 16. This longitudinal axis 18 maybe defined e.g. to be parallel to the side walls of the respectivetransducer recess 6, 7. The flow channel insert 12 comprises a first, asecond, and a third ultrasound reflector 8, 9, 10, which are positionedand oriented to reflect and guide and ultrasound signal emitted by thefirst ultrasound transducer 6, onto the second ultrasound transducer 7,which then can detect the ultrasound signal, and vice versa reflect orguide an ultrasound signal from the second ultrasound transducer to thefirst ultrasound transducer. The flow tube 20 has a first and a secondtube end opening 37, 38 and defines a flow channel 5 as an inner spacebetween the tube end openings 37, 38. During operation of the ultrasonicflow meter 1, the first and second tube end openings are connected to apiping system for moving said fluid. The fluid flows through the firsttube end opening, through the flow channel 5, and out through the secondtube end opening 37, 38, or the opposite direction. During the followingdescription, the fluid is described as flowing from the first to thesecond tube end opening 37, 38, but of course the fluid may flow in theopposite direction. An ultrasound signal is emitted from the firstultrasound transducer 6. The ultrasound signal moves through the slantedbottom wall 17 of the first transducer recess 15, through the fluid ontothe first ultrasound reflector 8, which reflects the ultrasound in adirection towards the second ultrasound reflector 9, which in turnreflects the ultrasound signal in a direction towards the thirdultrasound reflector 10. The third ultrasound reflector 10 reflects theultrasound signal towards to second ultrasound transducer 7. Theultrasound signal moved through the slanted bottom wall 17 of the secondtransducer recess 16 and onto the second ultrasound transducer 7, wherethe ultrasound signal is detected and converted into an electronicsignal, which is sent to the electronic circuit 4. Then, an ultrasoundsignal may be sent in the opposite direction, i.e. from the secondultrasound transducer 7 to the first ultrasound transducer 6, where thesignal is also converted into an electrical signal, which is sent to theelectronic circuit 4. By comparing the travel time of the two ultrasoundsignals, i.e. the temporal duration between the moment where theultrasound signal is emitted by the one transducer and until the momentit is detected by the other transducer, the velocity of the fluid may becalculated. Then by knowing the flow profile of the flow tube 20, theflow velocity is converted into a volume per time. Finally, by summingthis volume per time over time, the consumed volume is measured. Thesecalculations in some embodiments be performed by the electronic circuit4, but may also be performed at a central facility of the utilitycompany, i.e. the meter data such as travel times or other datarepresentative of travel times may be extracted from the meter by e.g.manual read-outs or using wireless technology, such as e.g. radiocommunication.

According to an embodiment of the invention, the velocity of the fluidflowing through the measurement chamber can be calculated on the basisof a measurement of the transit time (time-of-flight) from the firsttransducer to the second transducer and vice versa, preferably bymeasuring the difference in the two transit times. The relationshipbetween the transit times (t_(up)=transit time when the ultrasoundsignal propagates against the fluid flow, t_(down)=transit time when theultrasound signal propagates in the same direction as the fluid flow)and the flow velocity of the fluid may vary according to differentgeometries, i.e. with different flow paths ultrasound signal. However,it may typically apply that

$v_{fluid} \propto \frac{\Delta\; t}{t^{2}}$where v_(fluid) is the flow velocity of the fluid flowing through themeasurement chamber, Δt is the difference between the transit timeagainst the flow t_(up) and the transit time with the flow t_(down), andt is the transit time of the ultrasound signal. By increasing Δt therelative uncertainty of the measurement is decreased, however, byincreasing t the uncertainty is drastically reduced, as t participatesas squared. Therefore, the flow meter according to various embodimentshas reduced uncertainty in the measurement of v_(fluid), since both Δtand t are increased.

Here, it should be noted that this invention is not bound by the abovepresented theoretical presentation, which is merely presented toillustrate the advantages of the invention.

Referring to FIG. 2, an embodiment of the invention is illustrated.Further to the above described embodiment, the present embodimentillustrates an ultrasonic flow meter 1 prior to assembly of said meterhousing 2 with said flow tube 20. Here, it is can be seen that the firstand second transducer recesses 15, 16, in which the first and secondultrasound transducers 6, 7 are positioned, can be inserted into a firstand a second tube opening 21, 22 in the flow tube 20. In relation to theassembly of the ultrasonic flow meter 1, it can be seen on FIG. 2 thatthe flow channel insert 12 is positioned in a position such that thefirst and second tube opening 21, 22 in the flow tube 20 are positionednext to a first and a second insert opening 33, 34 in the flow channelinsert 12. Thereby, the first and second transducer recess 6, 7 is,during assembly of the ultrasonic flow meter 1, inserted into the firstand second tube openings 21, 22 in the flow tube 20 and into the firstand second insert openings 33, 34. Thereby, the positions of the flowtube 20 and the flow channel insert 12 are fixated with respect to eachother due to the engagement of the first and second transducer recesses6, 7 into the first and second tube openings 21, 22 and the first andsecond insert openings 33, 34. This fixation is, however, dependent onthe fixation of the meter housing 2 to the flow tube 20. This fixationmay be facilitated e.g. by insertion of one or more locking pins 11through engagement openings of the flow tube 20 and the meter housing 2.The setup of the present embodiment may advantageously reduce thepressure on the meter housing 2 from a fluid in the flow channel 5 sincethe size of the transducer recesses 15, 16 may be reduced due to theslanted positioning of the ultrasound transducers 6, 7, but this setupmay also induce a problem of how to electrically connect the electricalcircuit 4 with the transducers 6, 7. However, as is shown partly by themagnification, by means of a first elastic contacts 24, which are incontact with the upper surface 35 of the first transducer 6, and a metallayer contact 26, which are in contact with the emitting surface 36 ofthe first transducer 6, the first transducer 6 is put into electricalcontact with the electrical circuit 4. Similarly, the second transducer7 is put into contact with the electrical circuit 4 by means of thesecond elastic contact 25 and the metal layer contact 26. In the presentembodiment, a common metal layer contact 26 is used. However, inalternative embodiments two separate contacts may be used.

Now, referring to FIG. 3, an embodiment of the invention is illustrated.In FIG. 3, the ultrasonic flow meter 1 is shown before assembly, i.e.the individual parts can be seen. The meter housing 2 of the ultrasonicflow meter 1 is assembled from a number of different parts. A meterhousing body 32 has in the bottom a first and second transducer recess15, 16. The first and second transducer recesses 15, 16 are each adaptedto receive one of a first and second ultrasound transducer 6, 7. Thefirst and second transducer recesses 15, 16 have slanted bottom walls17, which results in the first and second ultrasound transducers 6, 7 tobe orientated such that their respective ultrasound emitting orreceiving surfaces are non-parallel to a longitudinal axis 19 of theflow channel 5 and non-orthogonal to longitudinal axes 18 of thetransducer recesses 15, 16. The meter housing 2 also comprises anelectronic circuit 4, which is in electrical contact with said first andsecond ultrasound transducers 6, 7 and with a battery 3. The electricalcontacts between the electrical circuit 4 and the first and secondultrasound transducers 6, 7 are in this embodiment established asfollows. A first and a second elastic contact 24, 25 is put into contactwith, in one end, the first and second ultrasound transducers,respectively, and, in the other end, the electrical circuit 4.Furthermore, a metal layer contact 26 established electrical contactbetween the bottom sides of said first and second ultrasound transducers6, 7 and the electrical circuit 4. According to the present embodiment,the electrical circuit 4 fixated in a first connection part 28, in whicha battery 3 supplying electrical power to the electrical circuit 4 mayalso be fixated. The first connection part 28 is connected to a secondconnection part 29, which together with a third connection part 30sandwich a part of the first and second elastic contacts 24, 25. Thethird connection part 30 may then be connection to the meter housingbody 32. Finally, the meter housing comprises a display 23 for showinge.g. consumption data, such as e.g. the instantaneous consumption rate,the accumulated consumption since the last readout and/or the totallifetime accumulated consumption, or other data, such as meteridentification number, production serial number etc. The display 23 isfixated to the meter housing body 32 by a display frame 27. The meterfurthermore comprises a flow tube 20 defining a flow channel 5 as thehollow inner space of the flow tube 20. The flow tube 20 has a firsttube end opening 37 in one end and a second tube end opening 38 in theopposite end. The fluid to be measured can then flow through the firsttube opening 37, through the flow channel 5, and out through the secondtube opening 38, or the opposite direction. Preferably, the flow tube 20can be connected to existing piping system, thereby allowing the fluidto flow through the flow channel 5. The meter housing 2 can be connectedto a fourth connection part 31 of said flow tube 20 by insertion oflocking pins 11, which connects the bottom of the meter housing 2 withthe fourth connection part of the flow tube 20. Finally, a flow channelinsert 12, which may preferably be assembled from two mirror-symmetricalhalf-parts, may be inserted into the flow channel 5. The two half-partsmay have insertion recesses for a first, second, and third ultrasoundreflectors, so that when the two half-parts are assembled into the flowchannel insert 12, the ultrasound reflectors are incorporated in thisflow channel insert 12. The flow channel insert 12 may, prior toassembly of the meter housing 2 with the flow tube 20 by the lockingpins 11, be inserted into the flow channel 5 in a position opposite orbelow the meter housing 2. The transducer recesses 15, 16 of the meterhousing 2 may be inserted into tube openings 21, 22 in the flow tube 20,and into insert openings 33, 34, which are formed in the flow channelinsert 12, when the two half-parts of this flow channel insert 12 areassembled. Thereby, the positions of the flow tube 20 and the flowchannel insert 12 relative to the meter housing 2 is fixated, at leastthe position in a direction parallel to a longitudinal axis 19 of theflow tube 20. The position of the meter housing 2 is finally fixated tothe flow tube 20 by means of two locking pins 11. These locking pins 11engage locking pin openings 39, which are positioned in the meterhousing 2 as well as in a fourth connection part 31 of the flow tube 2.According to the present embodiment, the ends of the two locking pins 11are adapted to engage each other and lock together. By means of saidlocking pins 11, the meter housing 2 is fixated to the flow tube 2.Furthermore, the transducer recesses 15, 16 fixate the flow tube 20 tothe flow channel insert 12. Thereby, the parts of the ultrasonic flowmeter 1 are fixated to each other.

Now referring to FIG. 4, an embodiment of the invention is illustrated.A part of the ultrasonic flow meter 1 is shown, including the flow tube20 defining a flow channel 5, a first and second transducer recess 15,16, in which a first and second transducer 6, 7 is positioned,respectively. Furthermore, a flow channel insert 12, including a first,second, and a third ultrasound reflector 8, 9, 10, and guide elements14, is shown. An ultrasound signal is emitted from the first ultrasoundtransducer 6 and reflected by the first, second, and third ultrasoundreflectors 8, 9, 10 onto the second ultrasound transducer 7, where theultrasound signal is detected and converted into an electrical signal.An ultrasound signal path 44 is shown from the first ultrasoundtransducer 6, via the ultrasound reflectors 8, 9, 10, and to the secondultrasound transducer 7. This ultrasound signal path 44 is of course tobe understood as representing the directions of propagation of theultrasound signal, but not as restricting the propagation of theultrasound signal to the exact path line 44, since the actual path ofcourse extends spatially around the path line 44. Also, a fluid flowline 42 is shown. This fluid flow line 42 illustrates the flow of thefluid medium through the flow channel 5. Here, the fluid flow line 42 isof course also to be understood as representing a direction of flow andnot spatially restricting as the flow of course extends over theavailable inner of the flow tube 20. Since guide elements 14 extendsinto the flow channel 5 between the ultrasound reflectors 8, 9, 10, thefluid flow may be redirected or guided as illustrated by the fluid flowline 42. The actual extent of the effect of the guiding elements 14 mayof course be very different than illustrated; typically the effect maybe less significant. Also, it should be noted that the fluid flow line42 is not left-right symmetric, but shifted towards the right of FIG. 4.This may be explained by the effect of the guide elements on the actualfluid flow being delayed or retarded. Due to change of fluid flowdirection as induced by the guide elements 14, the interaction betweenthe fluid and the ultrasound signal represented by path line 44 may beincreased. This is due to the fact that the interaction between theflowing fluid and ultrasound signal is proportional to the path-integralbetweenI∝∫ _(S) F(r)·drwhere I is the interaction, F is a vector field representing the fluidflow, r is the spatial coordinate, and S defines the path of theultrasound through the fluid between the two transducers 6, 7. Since aneffect of the guide elements 14 on the fluid flow is that it is to ahigher degree in the same direction as path of the ultrasound signalpath 44, the dot-product F(r)·dr is increased, resulting in an increasein the interaction I. An increase in the interaction I may beadvantageous since this caused the time difference Δt between thetransit-time back and forth to increase, which again results in a moreaccurate measurement result of the fluid flow velocity.

Referring to FIG. 5A and FIG. 5B, an embodiment of the invention isillustrated. On FIG. 5A an ultrasonic flow meter 1 comprising a flowtube 20, a meter housing, and a flow channel insert 12, is shown. Theseare shown without details, but it is to be understood that any elementsof the above described embodiments may be present in the presentembodiment. The flow channel insert 12 is positioned in the flow channel5 of the flow tube 12, so that first and second insert openings 33, 34are positioned opposite first and second tube openings 21, 22,respectively. Then, during assembly, the first and second transducerrecesses 15, 16 are inserted into the first and second tube openings 21,22, and, furthermore, at least partly into the first and second insertopenings 33, 34 of the flow channel insert 12. Thereby, the position ofthe flow channel insert 12 is fixated relative to the flow tube 5.However, to fixate the meter housing 2 to the flow tube 20, differentmethods may be used. In one embodiment, locking pins 39 may be insertedthrough openings in a part of the flow tube 2 and into an opening in themeter housing 2, or vice versa. For instance, two locking pins 39 may beused by inserting them from opposite sides of the meter housing 2 andthen connecting the two locking pins 39, e.g. by a ratchet-likeconnection. Furthermore, in an alternative embodiment, a protrusion of alocking pin may engage a recess of another locking pin, the meterhousing 2, and/or the flow tube 20, or vice versa. Furthermore, inanother alternative embodiment, a protrusion of a part of the meterhousing, such as the transducer recess may engage a recess in the flowtube 20, such as in a tube opening 21, 22, or in the flow channel insert12, such as in an insert opening 33, 34, or vice versa. When the meterhousing is fixated to the flow tube 20 or to the flow channel insert 12,the flow tube 5, the meter housing 2 and the flow channel insert 12 areall three locked together or fixated, due to the flow tube 20 and theflow channel insert 12 being locked together upon insertion of thetransducer recesses 15, 16 into the tube openings 21, 22.

Now, referring to FIG. 6, a cross-sectional view of a part of anultrasonic flow meter 1 according to an embodiment of the invention isillustrated. The ultrasonic flow meter 1 comprises a flow tube 20defining a flow channel 5 as an inner space, a meter housing 2, and aflow channel insert 12. The meter housing 2 comprises a first ultrasoundtransducer 6 in first transducer recess 15, and a second ultrasoundtransducer 7 in second transducer recess 16, both ultrasound transducers6, 7 abutting the slanted bottom walls 17 of the respective transducerrecesses 15, 16. The flow channel insert 12 comprises a first, a second,and a third ultrasound reflector 8, 9, 10. These ultrasound reflectors8, 9, 10 are positioned and oriented so as to reflect an ultrasoundsignal from said first ultrasound transducer 6 to said second ultrasoundtransducer 7 and vice versa. As can be seen from FIG. 6, the slantedbottom walls 17 each have a focusing interface 43 between the meterhousing 2 and the flow channel 5, here illustrated as a concave surface.The focusing effect may of course vary in different embodiments. Also,the focusing effect may in alternative embodiments be due to a focusinginterface between the transducer and the slanted bottom wall, or as acombination of focusing interfaces. By focusing an emitted ultrasoundsignal, a greater part of this ultrasound signal may reach the receivingultrasound transducer, thereby increasing the signal-to-noise ratio.Similarly, by focusing an ultrasound signal before the receivingtransducer, the signal-to-noise ratio may be increased.

Referring to FIGS. 7A, 7B, and 7C, an embodiment of the invention isillustrated. Each of FIGS. 7A, 7B, and 7C illustrate a part of anultrasonic flow meter, including a part of a meter housing 2, a flowtube 20 defining a flow channel 5, and one or more ultrasound reflectors8, 9, 10. These ultrasound reflectors 8, 9, 10 reflect an ultrasoundsignal emitted from the first ultrasound transducer 6 onto the secondultrasound transducer 7. The path 44 of the ultrasound signal isillustrated. As can be seen from FIGS. 7A, 7B, and 7C, the same meterhousing 2, including the same ultrasound transducers 6, 7 positioned andorientated identically in the meter housing 2, can be connected to aflow tube 20 of different diameter. However, the positions and/ororientations of the one or more ultrasound reflectors 8, 9, 10 canchanged for different sizes or diameters of flow tubes 20. Thisillustrates an advantage of the invention in that the same meter housing2 can be used for flow tubes 20 with different sizes or diameters.Furthermore, it is illustrated on FIG. 7C, only a signal ultrasoundreflector 8 is shown, illustrating that this may be advantageous forlarger sizes or diameters of flow tubes 20.

LIST OF REFERENCE NUMERALS

-   1. Ultrasonic flow meter-   2. Meter housing-   3. Battery-   4. Electronic circuit-   5. Flow channel-   6. First ultrasound transducer-   7. Second ultrasound transducer-   8. First ultrasound reflector-   9. Second ultrasound reflector-   10. Third ultrasound reflector-   11. Locking pin-   12. Flow channel insert-   14. Guide element-   15. First transducer recess-   16. Second transducer recess-   17. Slanted bottom wall-   18. Transducer recess longitudinal axis-   19. Flow channel longitudinal axis-   20. Flow tube-   21. First tube opening-   22. Second tube opening-   23. Display-   24. First elastic contact-   25. Second elastic contact-   26. Metal layer contact-   27. Display frame-   28. First connection part-   29. Second connection part-   30. Third connection part-   31. Fourth connection part-   32. Meter housing body-   33. First insert opening-   34. Second insert opening-   35. Upper surface-   36. Emitting surface-   37. First tube end opening-   38. Second tube end opening-   39. Locking pin openings-   40. Reflective surface-   41. Inserting said first and second transducer recesses-   42. Fluid flow line-   43. Focusing interface-   44. Ultrasound path-   45. Inserting said locking pin

What is claimed is:
 1. An ultrasonic flow meter comprising: a flow meterhousing including an enclosed area; an electronic circuit for operatingthe ultrasonic flow meter; a flow tube defining an inner flow channelfor a fluid to be measured; and one or more ultrasound reflectors,wherein the flow meter housing includes: a first ultrasound transducerdisposed within the enclosed area, a second ultrasound transducerdisposed within the enclosed area, a first transducer recess with afirst bottom wall, and a second transducer recess with a second bottomwall, wherein the first ultrasound transducer is positioned in the firsttransducer recess to propagate a signal through the first bottom wall,and the second ultrasound transducer is positioned in the secondtransducer recess to propagate a signal through the second bottom wall,and wherein the first bottom wall and the second bottom wall arefocusing.
 2. The flow meter according to claim 1, wherein the firstbottom wall and the second bottom wall are concave.
 3. The flow meteraccording to claim 1, wherein the first ultrasound transducer is inabutment with the first bottom wall, and the second ultrasoundtransducer is in abutment with the second bottom wall.
 4. The flow meteraccording to claim 1, wherein the first bottom wall and the secondbottom wall are slanted.
 5. The flow meter according to claim 1, whereinthe one or more reflectors are focusing.
 6. The flow meter according toclaim 1, wherein the flow meter further comprises a flow channel insertincluding guide elements for guiding the flow of the fluid, wherein theguide elements are adapted for extinguishing ultrasound.